Improve confusing comment for HeapTupleSatisfiesNow, per gripe from Greg Stark.

diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 5a19e12553d4b31a0cf76b9c8ac5975848297200..a3b52fa7eb436986aa25a5314590a4533a03c2ff 100644 (file)
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -32,7 +32,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.96 2006/09/03 15:59:39 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.97 2006/09/15 16:39:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -253,19 +253,18 @@ HeapTupleSatisfiesItself(HeapTupleHeader tuple, Buffer buffer)
  *
  * The satisfaction of "now" requires the following:
  *
- * ((Xmin == my-transaction &&                         changed by the current transaction
- *      Cmin != my-command &&                                  but not by this command, and
- *             (Xmax is null ||                                                the row has not been deleted, or
- *                     (Xmax == my-transaction &&                      it was deleted by the current transaction
- *                      Cmax != my-command)))                          but not by this command,
+ * ((Xmin == my-transaction &&                         inserted by the current transaction
+ *      Cmin < my-command &&                                   before this command, and
+ *      (Xmax is null ||                                               the row has not been deleted, or
+ *       (Xmax == my-transaction &&                    it was deleted by the current transaction
+ *        Cmax >= my-command)))                                but not before this command,
  * ||                                                                          or
- *
- *     (Xmin is committed &&                                   the row was modified by a committed transaction, and
+ *     (Xmin is committed &&                                   the row was inserted by a committed transaction, and
  *             (Xmax is null ||                                        the row has not been deleted, or
- *                     (Xmax == my-transaction &&                      the row is being deleted by this command, or
- *                      Cmax == my-command) ||
- *                     (Xmax is not committed &&                       the row was deleted by another transaction
- *                      Xmax != my-transaction))))                     that has not been committed
+ *              (Xmax == my-transaction &&                     the row is being deleted by this transaction
+ *               Cmax >= my-command) ||                        but it's not deleted "yet", or
+ *              (Xmax != my-transaction &&                     the row was deleted by another transaction
+ *               Xmax is not committed))))                     that has not been committed
  *
  *             mao says 17 march 1993:  the tests in this routine are correct;
  *             if you think they're not, you're wrong, and you should think